1. Field of the Invention
This invention relates generally to electrical pulse signal generators and more particularly to a sub-nanosecond, kilovolt pulse generator for use in impulse radar apparatus, active electromagnetic signal jammers, and relatively high power microwave weapon systems.
3. Description of the Prior Art
In recent years there has been active research activity into the generation of nanosecond type pulses utilizing a high power photoconductive solid state switch coupled to a storage device. One of the critical elements of high power pulse generation with sub-nanosecond pulsewidth is the switch. To generate such pulses, the switch must exhibit a transition from a high resistivity state to a conductive state in a sub-nanosecond time interval. One such switch is disclosed in U.S. Pat. No. 5,028,971 issued to Anderson H. Kim et al on Jul. 2, 1991, and entitled, "High Power Photoconductor Bulk GaAs Switch". The teachings of this patent are intended to be incorporated herein by reference and discloses a photoconductive gallium arsenide (GaAs) switch having two mutually opposite grided electrodes which receives activating light from a laser. When the laser light is applied to the switch, the electrical resistance of the semiconductive material is decreased through electron/hole pairs being generated. This resistance change is translated into a change in the current that flows through an output circuit.
The other critical element in the generation of fast electrical pulses utilizing high power photoconductive solid state switches is the energy storage element. Depending on the structure, it produces not only sub-nanosecond pulsewidth, but also voltage enhancement.
In general, two techniques are used to generate and deliver fast rise time, high power pulses to a load impedance The first technique utilizes the recombination property of the semiconductor material from which the switch itself is fabricated The pulses generated with this technique using photoconductive GaAs switches typically have a long pulsewidth with a relatively long recovery time at high bias voltage. This is due to the substantially long recombination time and the switch lock-on phenomenon exhibited by gallium arsenide In the second approach, the output pulsewidth is controlled by the energy storage element which may comprise either a short section of transmission line or capacitor which delivers all or substantially most of the stored energy to the load so that only a closing photoconductive switch is required.